Light experience during development affects asymmetry of forebrain function in chickens.

The chicken brain has asymmetry of forebrain function of attack and copulation behaviors. This study reports that this asymmetry, revealed by intracranial injections of glutamate, is affected by light exposure. Eggs were incubated in 3 forced-draught incubators matched for noise, humidity and temperature control, so that light and laboratory noise were the only systematic variables. All eggs were incubated in darkness for the first 17 days of incubation after which they were allocated to one of 3 incubating conditions, L+S+, L-S+, L+S-, where + or - indicates the presence or absence of light (L) or laboratory noise (S). Light exposure was necessary to establish lateralization of attack and copulation, sound was not since only the L+S+ and L+S- groups were lateralized. The lateralization of auditory habituation was not affected by these incubating conditions. Further experiments established that on day 19 of incubation exposure for 4 h to a light of constant intensity produced lateralization. 1 h exposure to a light of constant intensity or to a flickering light (1.7 Hz) failed to produce lateralization. Examination of the data for individuals suggests that light exposure synchronizes the direction of lateralization rather than generates its presence. Environmental and genetic factors interact to produce the lateralization of attack and copulation.